It is known that the best and easiest oilseed to process is soy bean. Canola.RTM. and rapeseed have also been processed on the kind of equipment used to process soy bean; however, they have been ground, cooked, and rolled into flakes to provide an extractable material. Generally Canola.RTM. flakes can be run only at a much slower rate than soy beans. The resultant rapeseed and Canola.RTM. residual material after oil removal, called "marc", cannot readily be used for animal feeding due to the presence of trypsin inhibitors, high euric acid and high glucosinolates.
The process and apparatus of the present invention can be used to process oil seeds such as soy bean and safflower; however, the apparatus is particularly beneficial in obtaining oil from granular sources such as rice bran, wheat mill feed, Canola.RTM., rapeseed in general, and amaranth (as well as similar grains), which have lower oil content than soy bean and safflower and, except for Canola, have not been economically competitive as an oil source prior to the present process. Typically, oil seeds contain from about 15 percent to about 40 percent by weight oil. Most of the grains of the kind described above contain only from about 4 percent to about 20 percent by weight oil. In addition to the lower oil content, the granular materials frequently require special processing in preparation for oil removal, and when a grain oil source such as rice bran is used, the rice bran itself has a limited shelf life before the oils begin to degrade, due to particularly active enzymes present in the bran. Thus, there are particular handling requirements and processing requirements necessary to enable the use of such edible oil sources.
Edible oils are usually extracted from most oil seeds by soaking crushed or pulverized seeds in liquid hexane. Usually, the seeds are washed with hexane five to seven times to get the maximum recovery of oil. The amount of hexane required for such washing is quite high, up to 40 times the weight of oil recovered. The oil is then separated from the oil-hexane solution, or "miscella" by distillation, and the hexane solvent is recovered for recycle use in the separation process. The marc which remains after removal of the oil from the seeds is generally a powder and contains substantial amounts, up to about 40 percent, of hexane. The marc is then "dried" to recover the residual hexane. Recovery of the hexane from the miscella and from the marc are both energy intensive processes and require extensive capital equipment, and is particularly expensive because of the large amount of hexane required.
As previously discussed, Canola.RTM. and rapeseed in general have been processed on soy bean equipment; they have been ground, cooked and rolled into flakes prior to oil extraction. Even then, the process rate in oil seed processing equipment was marginally cost effective compared with soy bean. Other potential vegetable matter sources of oil include wheat mill feed, amaranth, and rice bran, for example. Wheat mill feed is the material removed from wheat during milling. Twenty percent or more of all the world's wheat ends up as mill feed. Most of this goes into pet food and animal feed. Amaranth, another potential source of oil, known in the midwest as "pig weed", grows wild. The amaranth cultivars are available to anyone through the U.S.D.A. Wheat mill feed and amaranth can both be extruded into a pellet because they contain sufficient amounts of starch and sugars. The pellets can be processed on standard soy bean equipment, but the hexane solvent typically used for extraction also extracts large quantities of green chlorophyll so that the oil is difficult to refine as well as being dark green, almost black in color.
Rice bran requires a particularly specialized process. The rice bran cannot easily be flaked or made into an extrudable pellet because of lack of starch and the presence of sucrose. Rice bran can be extruded if corn starch is added, but the sucrose can caramelize if heated in the presence of air, giving a dark hue to the oil product. Rice oil can be extracted with hexane using an extractor of the type used to process soy beans, but this process is comparatively slow, energy intensive and expensive when compared to soy beans. Moreover, the remaining rice bran flour still has substantial oil in it.
Examples of equipment and processes for extracting oil from vegetable matter include the following:
U.S. Pat. No. 4,353,837, to Roy W. Barns, issued Oct. 12, 1982, describes apparatus and method for extracting oil from pelletized grain material in which the grain pellets are fed into a liquid miscella of solvent and oils removed from the feed, and then passed downwardly in a column countercurrent to an upward flow of solvent vapor, with additional liquid solvent being added to the feed material near the bottom of the column.
U.S. Pat. No. 2,448,729, to A. K. Ozai-Durrani, issued Sep. 7, 1948, describes a method of extracting oil from rice bran and rice polish. The rice bran or polish or mixtures of the two is subjected to an agglomeration step immediately, or within a relatively short time interval, after the bran and polish have been removed from the rice grain. The natural sugars, starches and glutens of the rice bran are partially soluble in water and are used to aggregate the material into porous aggregates suitable for oil extraction processes. Typically the aggregate material is extruded into elongated relatively thin strips. The aggregated rice bran or polish in then extracted using a vegetable oil solvent, preferably hexane, under a reduced pressure or in the presence of an inert gas such as nitrogen or carbon dioxide, and at a maximum temperature of about 140.degree. F. to avoid decomposition of the vitamin and food values of the material.
U.S. Pat. No. 2,727,914, to E. A. Gastrock et al., issued Dec. 20, 1955, describes the solvent extraction of rice bran to produce bran oil. In particular, the rice bran is subjected to a mild heat treatment to make the oil more easily extractable. The rice bran particles are cooked while controlling their moisture content so that, at least at an early stage, the particles contain between about 14% to 26% by weight moisture. The cooking temperature is increased from about 170.degree. F. to about 235.degree. F. in the final stage, at which time the moisture content has decreased to between about 6% to about 18%, by weight. The resulting bran particles are then exposed to a relatively cool atmosphere conducive to the evaporation of moisture until they undergo a substantially uniform decrease in temperatue to below about 130.degree. F. and a moisture content ranging from about 2% to about 4%. The treated rice bran particles are then mixed with a solvent for rice bran oil and the resulting slurry is filtered to separate the rice bran particles from the miscella. Solvents recommended for extraction include commercial hexanes, methylpentanes and trichloroethylene.
U.S. Pat. No. 2,829,055, to A. K. Ozai-Durrani, issued Apr. 1, 1958, pertains to a method of treating rice paddy or hulled rice grains to remove the rice oils and fats from the bran and polish coatings of the rice. The process for removing the rice oil content of the bran coating on dehulled rice grains comprises immersing the whole grains in a solvent consisting of a low specific gravity petroleum fraction for a time interval at a temperature less than the boiling point of the solvent, to obtain extraction of the significant portion of the rice oil content of the bran coating. In another embodiment of the invention, the removal of the hulls from the rice paddy is accomplished as a sequence of the defatting treatment. The rice paddy is extracted with an organic solvent, and the majority of the solvent, containing oils, is removed. The solvent is removed by drainage, with residual solvent being removed from the rice grains either by vacuum distillation, or by heating the grains to a temperature above the boiling point of the solvent, or by exposing the grains to a current or blast of air. The solvent-containing paddy is then shocked by suddenly increasing the temperature by between about 10.degree. C. and 50.degree. C. to substantially the flash point of the solvent and then igniting the solvent with a flame or spark, to burn the hulls, which fall from the rice kernel, leaving the kernel intact and unbroken.
U.S. Pat. No. 3,261,690, to T. B. Wayne, issued Jul. 19, 1966, relates to improvements in the milling of rice and barley which greatly reduces the breakage of rice grains during the milling. In general, the bran is milled from brown rice in the presence of a solvent effective to extract fatty components from the rice and germ. The bran may be softened with a liquid bran-softening agent used in combination with a volatile organic solvent effective to extract fatty components from the bran and germ. Examples of softening agents include non-toxic oils such as highly refined mineral oils and edible vegetable oils, as well as naturally occurring or synthetic esters of glycerol, propylene glycol, polypropylene glycol or sorbitol with fatty acids. Among preferred extraction solvents are low boiling, highly refined petroleum fractions such as n-hexane and n-heptane. In addition, polar solvents such as alcohols and ethers may be used. Chlorinated hydrocarbons may also be used.
U.S. Pat. No. 3,271,160, to G. A. Kopas et al., issued Sep. 6, 1966, describes a process for preparing feed from undecorticated oil free safflower seed residue. The safflower seeds are crushed or otherwise broken open to get access to the oil inside them, which oil is solvent extracted using known techniques, preferably with hexane. The improvement provided by the invention is that the meat of the residual seed materials, after extraction, can be separated from the hulls by subjecting the relatively dry residual seeds to impact--either pneumatically or by shooting it in an air stream through a gun at a target or mechanically, as in a vertical or horizontal impact mill or similar device. Since the meat particles are fractured more than the hulls, a classification by size alone can be used to separate the products into markedly different protein content compositions.
U.S. Pat. No. 4,808,426, to Strop et al., issued Feb. 28, 1989, describes a process for extraction of vegetable oil from an oil bearing material such as soy bean, corn and the like. The process comprises adding at least one reagent and an oil, of preferably the same type as will be extracted from the oil bearing material, to the oil bearing material to form a slurry mixture. The reagent preferably comprises a reagent for cleaving the chemical bond of the non-hydratable phospholipids, thereby converting the non-hydratable phospholipids into hydratable phospholipids. Typically this reagent is an acid. The slurry is heated at a preselected temperature for a period of time, preferably under a partial vacuum. Subsequently, the resultant oil is extracted from the slurry mixture. This process reduces the phospholipid and trace metal content in the oil extracted from the oil bearing material.
U.S. Pat. No. 5,035,910, to J. D. Jones et al., issued Jul. 30, 1991, pertains to separation of oilseed components in solvent phase. In particular, oilseed, particularly whole Canola.RTM. seed, is separated under non-oxidizing conditions, in a non-aqueous solvent system, into high quality oil and proteinaceous flour food components, and a seed coat meal (hull) byproduct. Maceration in a solvent, sequential liquid cyclone separations, and recovery of components and solvent all take place in completely enclosed liquid flow-through systems with solvent recycle, in a relatively short time. Flaking, cooking and pressing of the Canola.RTM. seed is not required.
U.S. Pat. No. 5,047,254, to T-C Lee, issued Sep. 10, 1991, describes a process for the recovery of edible oil from cereal products. The oil content of rice bran is stabilized by simultaneous high temperature high pressure treatment. Such a treatment also improves the yield obtainable when such oil is extracted from rice bran by solvent extraction. The bran is pretreated prior to extraction of oil by subjecting the bran to 100.degree. C. to 200.degree. C. and at least 500 psi for from 5 to 20 seconds in the absence of added moisture. The pelletized product produced is then extracted using known solvent extraction methods.
Each of the above-described methods and apparatus for separating oil from vegetable matter has both advantages and disadvantages. The present invention provides a very economical method and apparatus for extracting oil from vegetable matter, providing cost advantages over currently utilized techniques. Oil is extracted in a fraction of the time required for previously used commercial methods, and to a substantially greater degree. By use of the process of the present invention, rice bran can be produced which has an oil content of less than two percent, and has no objectionable odor or taste, so that it is suitable for use in human food products. Further, the present invention results in the production of high quality oils at a cost substantially less than is possible with present commercial processes.